Signal Averaging; Measuring Over-Range Samples; Sample Dilution - Hach 2100N Instruction Manual

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SECTION 2,
continued

2.7 Signal Averaging

2.8 Measuring Over-Range Samples

2.8.1 Sample Dilution

Figure 5 Filtering Apparatus
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The signal averaging feature provides compensation for reading fluctuations
caused by random drifting particles in the sample. Signal averaging may be turned
on or off at any time during measurement by pressing the
on, the signal averaging annunciator is lighted. The display is updated
approximately once every second.
Turning on signal averaging causes ten measurements to accumulate in a
measurement buffer. The initial value is displayed immediately. Subsequent
values are an average of readings accumulated in the buffer. After measurements
are accumulated, the displayed value is a moving average of the specified number
of measurements in the averaging buffer. Select signal average OFF for optimum
response time. Pressing
ENTER
an updated display. If power is turned off and then restored, the instrument
defaults to the signal averaging condition selected during the last measurement.
The nephelometric method of turbidity measurement depends on light scattering
from suspended particles. If turbidity is very high, significant amounts of light
may be absorbed by the particles, and little light is available for scattering. This
results in a negative interference; the measured turbidity is lower than the actual
turbidity. This condition is called "going blind."
Light absorbing particles, such as activated carbon and significant amounts of true
color, also may cause an instrument to "go blind." Dilution may not be effective in
correcting for these interferences.
When too much light is absorbed by the sample matrix, sufficient light may not be
available for measurement. If this condition occurs, the lamp icon on the
instrument display flashes to warn the user.
High turbidity samples may be diluted, but avoid this when possible because
dilution may alter the characteristics of the suspended particles and produce
erroneous results.
When necessary, dilute the sample with a portion of filtered sample. Diluting with
distilled or deionized water may dissolve some of the turbidity.
Filter samples with the Sample Filtration and Degassing Kit (Cat. No. 43975-10)
shown in Figure 5. If the filters plug too rapidly, use a standard 47 mm filtration
apparatus illustrated in Figure 6 with a membrane filter (Cat. No. 13530-01), or
use a glass-fiber filter (Cat No. 2530-00) for very high solids.
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SIGNAL AVG
clears the buffer of all stored values and provides
key. When